The city of Quy Nhon in central Vietnam is expanding towards the nearby Thi Nai Lagoon. The Rockefeller Foundation supported restoration of mangrove forests along the shore of the lagoon to protect it from erosion, and help limit urban development in these areas. Mangrove forests were planted in 5 villages. In Vinh Quang village seedling survival was about 80%, in Diem Van 50% and in Nhan An there were no surviving seedlings after two years. This paper describes mangrove seedling plantation and protection activities implemented by these three communities, and compares their experience to explain why there were significant differences in outcomes. Similar co-management approaches were employed in each case, but there were significant differences in the prior familiarity of villagers with mangroves, their dependence on aquatic harvesting, the consistency with which informal tenure rights of different groups were recognized, the quality of local leadership for mangrove planting and protection, and the quality of habitat for mangrove seedlings. Results showed that simply adopting consistent processes for co-management did not secure consistent outcomes, and that local forest management authorities failed to adopt a mechanism for long-term benefit sharing.